Just an FYI, with Darkness mode when you use the gas mask it makes the screen go black. You can still play, and any HUD is still visible, but you can't see the game world.

I'm seeing this too. If you enable Darkness mode while the gas mask is equipped it works fine, but when you start taking the gas mask off and on, or hit some scripted events it goes black for me too.

Sometimes taking the gas mask off restores the screen, but you can only go so far by putting it on and taking it off. Turning the option off has never fixed it for me, I've always had to reload the game.